A useful therapeutic method for the treatment of malignancies is the administration of compounds that stimulate the differentiation of malignant cells to normal cells, thereby inhibiting and/or reversing the malignant transformation. Thus, it has been shown by Suda et al. (U.S. Pat. No. 4,391,802) that 1.alpha.-hydroxyvitamin D compounds (e.g. specifically 1.alpha., 25-dihydroxyvitamin D.sub.3 and 1.alpha.-hydroxyvitamin D.sub.3) possess, for example, potent antileukemic activity by virtue of inducing the differentiation of malignant cells (specifically leukemia cells) to non-malignant macrophages (monocytes). Hence, these compounds are useful for the treatment of certain malignancies, specifically for the treatment of leukemia (Suda et al., U.S. Pat. No. 4,391,802). When used for such treatment, however, these known 1.alpha.-hydroxyvitamin D compounds have the disadvantage that they are also very potent calcemic agents, i.e. they cause elevated blood calcium levels by stimulating intestinal calcium absorption and bone calcium resorption. This calcemic activity represents, indeed, the well-known, classical function of these compounds. Furthermore, the cell differentiation activity (and, hence, antileukemic activity) of these compounds correlates with their calcemic activity. For example 1,25-dihydroxyvitamin D.sub.3, the most potent compound in inducing the differentiation of malignant cells to macrophages, is also the most potent vitamin D metabolite in stimulating calcium transport or raising serum calcium levels. For practical use as cell-differentiating agents, this potent calcemic activity is, of course, an undesired side effect, since the doses required for efficacy in diffentiating malignant cells can lead to excessively high and non-physiological serum calcium levels in the treated subjects.